Location-independent raid group virtual block management

ABSTRACT

A computer storage system is described. A range of volume block numbers (VBNs) is assigned to a volume. A range of storage device block numbers (DBNs) is assigned to each of a plurality of storage devices. A first mapping parameters are created to map a first range of VBN numbers to a first selected range of DBNs using a first portion of a new storage device. A second mapping parameters are created to map a second range of VBN numbers to a second range of DBNs on a second portion of the new storage device.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/497,590 filed on Aug. 2, 2006, entitled LOCATION-INDEPENDENT RAID GROUP VIRTUAL BLOCK MANAGEMENT, by Strange et al., now issued as U.S. Pat. No. 7,660,966 on Feb. 9, 2010, which is a continuation of U.S. patent application Ser. No. 10/394,890 filed on Mar. 21, 2003, entitled LOCATION-INDEPENDENT RAID GROUP VIRTUAL BLOCK MANAGEMENT, by Strange et al., now issued as U.S. Pat. No. 7,111,147 on Sep. 19, 2006.

FIELD OF THE INVENTION

The present invention relates to storage systems and, more specifically, to a technique for mapping the capacity of storage devices into any RAID group of a storage system.

BACKGROUND OF THE INVENTION

A storage system typically comprises one or more storage devices into which data may be entered, and from which data may be obtained, as desired. The storage system includes a storage operating system that functionally organizes the system by, inter alia, invoking storage operations in support of a storage service implemented by the system. The storage system may be implemented in accordance with a variety of storage architectures including, but not limited to, a network-attached storage environment, a storage area network and a disk assembly directly attached to a client or host computer. The storage devices are typically disk drives organized as a disk array, wherein the term “disk” commonly describes a self-contained rotating magnetic media storage device. The term disk in the context is synonymous with hard disk drive (HDD) or direct access storage device (DASD).

Storage of information on the disk array is preferably implemented as one or more storage “volumes”, defining an overall logical arrangement of disk space. The disks within a volume are typically organized as one or more groups, wherein each group is operated as a Redundant Array of Independent (or Inexpensive) Disks (RAID). Most RAID implementations enhance the reliability/integrity of data storage through the redundant writing of data “stripes” across a given number of physical disks in the RAID group, and the appropriate storing of redundant information with respect to the striped data. The redundant information may thereafter be retrieved to enable recovery of data lost when a storage device fails.

In the operation of a disk array, it is anticipated that a disk can fail. A goal of a is high performance system is to make the mean time to data loss as long as possible, preferably much longer than the expected service life of the system. Data can be lost when one or more disks fail, making it impossible to recover data from the device. Typical schemes to avoid loss of data include mirroring, backup and parity protection. Mirroring stores the same data on two or more disks so that if one disk fails, the “mirror” disk(s) can be used to serve (e.g., read) data. Backup periodically copies data on one disk to another disk. Parity schemes are common because they provide a redundant encoding of the data that allows for loss of one or more disks without the loss of data, while requiring a minimal number of disk drives in the storage system.

Parity protection is used in a computer system to protect against loss of data on a storage device, such as a disk. A parity value may be computed by summing (usually modulo 2) data of a particular word size (usually 1 bit) across a number of similar disks holding different data and then storing the results on the disk(s). That is, parity may be computed on 1-bit wide vectors, composed of bits in predetermined positions on each of the disks. Addition and subtraction on 1-bit vectors are an equivalent to exclusive-OR (XOR) logical operations; these addition and subtraction operations can thus be replaced by XOR operations. The data is then protected against the loss of any one of the disks, or of any portion of the data on any one of the disks. If the disk storing the parity is lost, the parity can be regenerated from the data. If one of the data disks is lost, the data can be regenerated by adding the contents of the surviving data disks together and then subtracting the results from the stored parity.

Typically, the disks are divided into parity groups, each of which comprises one or more data disks and a parity disk. The disk space is divided into stripes, with each stripe containing one block from each disk. The blocks of a stripe are usually at equivalent locations on each disk in the parity group. Within a stripe, all but one block contain data (“data blocks”) with the one block containing parity (“parity block”) computed by the XOR of all the data. If the parity blocks are all stored on one disk, thereby providing a single disk that contains all (and only) parity information, a RAID-4 implementation is provided. If the parity blocks are contained within different disks in each stripe, usually is in a rotating pattern, then the implementation is RAID-5. The term “RAID” and its various implementations are well-known and disclosed in A Case for Redundant Arrays of Inexpensive Disks (RAID), by D. A. Patterson, G. A. Gibson and R. H. Katz, Proceedings of the International Conference on Management of Data (SIGMOD), June 1988.

The storage operating system of the storage system may implement a file system to logically organize the information stored on the disks of a volume as a hierarchical structure of directories, files and blocks. The storage operating system may also include a RAID subsystem that manages the storage and retrieval of the information to and from the disks in accordance with input/output (I/O) operations. There is typically a one-to-one mapping between the information stored on the disks in, e.g., a disk block number (DBN) space, and the information organized by the file system in, e.g., volume block number (VBN) space. The file system consists of a contiguous range of VBNs from zero to N, for a file system of size N-1 blocks. The storage operating system may further include administrative interfaces, such as a user interface, that enable operators (system administrators) to access the system in order to implement, e.g., configuration management decisions.

Configuration management in the RAID subsystem generally involves a defined set of modifications to the topology or attributes associated with a storage array, such as a disk, a RAID group (parity group), a volume or set of volumes. Examples of these modifications includes, but are not limited to, disk addition, disk failure handling, volume splitting, volume online/offline and changes to a RAID group size. The RAID group size is the maximum number of disks that may be contained within a RAID group. For example, if a RAID group size is “3”, then the number of disks in the group can be less than or equal to 3, but not more than 3. The RAID group size is typically a property of a volume, such that all RAID groups of the volume typically have the same RAID group size. When the RAID group reaches the maximum number, a new RAID group is created upon the addition of new disks.

Volume capacity is typically linked to the linear growth of the RAID groups that, is in turn, are organized linearly within the VBN space of a volume. Linear growth and organization of volume capacity is generally due to prior RAID subsystem support for only one contiguous VBN-to-DBN mapping range across all disks of a RAID group. Thus if the maximum RAID group size is increased, it is generally not possible to insert disks into the middle of the linear list of RAID groups. Moreover, a prior approach supports only one contiguous DBN-to-VBN mapping range on each disk of the RAID group, typically because the entire DBN space on the disk is mapped into the VBN space of the volume. If a disk in an existing RAID group (other than the “last” RAID group) is exchanged for a larger disk, it is generally not possible to make use of the additional space on the larger disk. For example, if a disk of a RAID group failed and was replaced with a larger disk, the additional space on the larger disk could not be used. The larger replacement disk could only use the VBN range that was previously allocated to the failed disk.

These restrictions also make it difficult to dynamically expand the storage space of an existing file system when upgrading from smaller disks of a volume to larger disks and then utilizing the additional capacity for the volume. An example of a prior approach used to upgrade smaller disks of a storage system to larger disks involves creating a new volume with the larger disks and copying the data from the smaller disks to the larger disks in accordance with, e.g., a volume copy operation. Thereafter, the data stored on the smaller disks are deleted and those disks are removed from the storage system. This approach represents a time consuming procedure that involves a period of time during which the data is not accessible by a client.

Often it is desirable to migrate smaller disks of a volume to larger disks in accordance with a synchronous capacity upgrade for a storage system that supports synchronous RAID mirroring. However, a prior approach used to perform such a synchronous capacity upgrade results in system downtime or client reconfiguration. For example, assume that it is desired to “mirror” an existing volume with disks of capacity size X to a new volume with disks of capacity 2X. A prior approach involves creation of an entirely new volume and copying of the data from the old volume to the new volume in accordance with the volume copy operation.

Since a new volume is created, that volume has a name that is different from the original volume. Moreover, the original volume is brought offline for a discrete period of time in order to ensure consistency of information that is written to the new volume during the copy operation. As a result, the file system is aware of the configuration change, as not only is the file service temporarily disrupted but a renaming operation occurs that renames the newly created volume to that of the original volume. In addition, the file system identifier must be changed and other “house keeping” duties must be performed to ensure that the operators/clients are not aware that their data has moved.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art by providing a technique for mapping the capacity of storage devices, such as disks, into any RAID group of a volume of a storage system regardless of the location of the RAID group within a volume block number (VBN) space of the volume. To that end, the inventive technique separates disks and mapped VBN ranges, allowing for flexibility in the description and extension of RAID group capacities, while providing disk addition policies that support location-independent disk insertion into RAID groups. The inventive technique also provides a disk label structure that supports the provision of multiple VBN ranges within a RAID group and within individual disks. Moreover, the technique provides file system support for allocation and topology management of the multiple mapped VBN ranges within disks and RAID groups, as well as noncontiguous VBN ranges across the RAID groups in the volume.

According to an aspect of the inventive technique, “raidmap” data structures are used to map VBN ranges into a disk block number (DBN) space of each disk. The raidmap is maintained by a RAID subsystem of the storage system and stored in the disk label structure, i.e., a RAID label, on the disk. Another aspect of the technique relates to the mapping of multiple VBN ranges to the DBN space of a disk through the ability to store more than one raidmap in a RAID label on each disk. Each raidmap comprises mapping parameters, such as a base offset into a VBN range of a volume, a base offset is into a DBN range of the disk and a size of the DBN-to-VBN mapping, used to describe the topology of the volume. These mapping parameters enable separation of DBN ranges on a disk from mapped VBN ranges of the volume. A write allocator of the file system uses the raidmap and its description of that topology to issue I/O operations when accessing data stored in the VBN range of a volume. Notably, the write allocator uses the mapping parameters of the raidmap to determine the noncontiguous VBN-to-DBN mapping of a disk within a RAID group. A topology mechanism exports the raidmap information from the RAID subsystem to the write allocator.

Advantageously, the present invention isolates disks from VBN ranges, providing flexibility in RAID group topologies. Isolation of VBN ranges from disks further allows for dynamic extension of the VBN range at the RAID level without requiring reorganization of the existing blocks in the file system. The inventive technique supports dynamic extension of capacity using existing, but formerly unused, disk space. Moreover, the on-disk label structure contains placeholders for multiple per-disk VBN range data, thereby facilitating instantiation of the raidmap information when a volume is brought into the system during initialization.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identical or functionally similar elements:

FIG. 1 is a schematic block diagram of an environment including a storage system that may be advantageously used with the present invention;

FIG. 2 is a schematic block diagram of a storage operating system that may be advantageously used with the present invention;

FIG. 3 is a schematic block diagram illustrating processes and threads of a RAID subsystem of the storage operating system of FIG. 2;

FIG. 4 is a schematic block diagram of an in-core representation of an embodiment of a RAID configuration tree in accordance with a configuration management framework is that may be advantageously used with the present invention;

FIG. 5 is a schematic block diagram of a file system map that may be advantageously used with the present invention;

FIG. 6 is a schematic block diagram illustrating the format of a disk coupled to the storage system of FIG. 1;

FIGS. 7A-7E are schematic diagrams of raidmaps that may be advantageously used with the present invention; and

FIG. 8 is a schematic block diagram of an in-core representation of another embodiment of a RAID configuration tree in accordance with the configuration management framework.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

FIG. 1 is a schematic block diagram of an environment 100 including a storage system 120 that may be advantageously used with the present invention. The storage system is a computer that provides storage service relating to the organization of information on storage devices, such as disks 130 of a disk array 160. The storage system 120 comprises a processor 122, a memory 124, a network adapter 126 and a storage adapter 128 interconnected by a system bus 125. The storage system 120 also includes a storage operating system 200 that preferably implements a file system to logically organize the information as a hierarchical structure of directories, files and virtual disks (hereinafter “blocks”) on the disks.

In the illustrative embodiment, the memory 124 comprises storage locations that are addressable by the processor and adapters for storing software program code and data structures associated with the present invention. For example, a portion of the memory may be organized as a “raidmap” cache 170 having locations used to store mapping data structures in accordance with the present invention. The processor and adapters may, in turn, comprise processing elements and/or logic circuitry configured to execute the software code and manipulate the data structures. Storage operating system 200, portions of is which are typically resident in memory and executed by the processing elements, functionally organizes the system 120 by, inter alia, invoking storage operations executed by the storage system. It will be apparent to those skilled in the art that other processing and memory means, including various computer readable media, may be used for storing and executing program instructions pertaining to the inventive technique described herein.

The network adapter 126 comprises the mechanical, electrical and signaling circuitry needed to connect the storage system 120 to a client 110 over a computer network 140, which may comprise a point-to-point connection or a shared medium, such as a local area network. Illustratively, the computer network 140 may be embodied as an Ethernet network or a Fibre Channel (FC) network. The client 110 may communicate with the storage system over network 140 by exchanging discrete frames or packets of data according to pre-defined protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP).

The client 110 may be a general-purpose computer configured to execute applications 112. Moreover, the client 110 may interact with the storage system 120 in accordance with a client/server model of information delivery. That is, the client may request the services of the storage system, and the system may return the results of the services requested by the client, by exchanging packets 150 over the network 140. The clients may issue packets including file-based access protocols, such as the Common Internet File System (CIFS) protocol or Network File System (NFS) protocol, over TCP/IP when accessing information in the form of files and directories. Alternatively, the client may issue packets including block-based access protocols, such as the Small Computer Systems Interface (SCSI) protocol encapsulated over TCP (iSCSI) and SCSI encapsulated over Fibre Channel (FCP), when accessing information in the form of blocks.

The storage adapter 128 cooperates with the storage operating system 200 executing on the system 120 to access information requested by a user (or client). The information may be stored on any type of attached array of writable storage device media such as video tape, optical, DVD, magnetic tape, bubble memory, electronic random access memory, micro-electro mechanical and any other similar media adapted to store information, including data and parity information. However, as illustratively described herein, the information is preferably stored on the disks 130, such as HDD and/or DASD, of array 160. The storage adapter includes input/output (I/O) interface circuitry that couples to the disks over an I/O interconnect arrangement, such as a conventional highperformance, FC serial link topology.

Storage of information on array 160 is preferably implemented as one or more storage “volumes” that comprise a collection of physical storage disks 130 cooperating to define an overall logical arrangement of volume block number (VBN) space on the volume(s). Each volume is generally, although not necessarily, associated with its own file system. The disks within a volume/file system are typically organized as one or more groups, wherein each group is operated as a Redundant Array of Independent (or Inexpensive) Disks (RAID). Most RAID implementations, such as a RAID-4 level implementation, enhance the reliability/integrity of data storage through the redundant writing of data “stripes” across a given number of physical disks in the RAID group, and the appropriate storing of parity information with respect to the striped data. Although a RAID-4 level implementation is illustratively described herein, it should be understood that other types and levels of RAID implementations may be used in accordance with the inventive principles described herein.

To facilitate access to the disks 130, the storage operating system 200 implements a write-anywhere file system that cooperates with virtualization modules to “virtualize” the storage space provided by disks 130. The file system logically organizes the information as a hierarchical structure of named directories and files on the disks. Each “ondisk” file may be implemented as set of disk blocks configured to store information, such as data, whereas the directory may be implemented as a specially formatted file in which names and links to other files and directories are stored. The virtualization modules allow the file system to further logically organize information as a hierarchical structure of blocks on the disks that are exported as named logical unit numbers (luns).

In the illustrative embodiment, the storage operating system is preferably the NetApp® Data ONTAP™ operating system available from Network Appliance, Inc., Sunnyvale, Calif. that implements a Write Anywhere File Layout (WAFL™) file system. However, it is expressly contemplated that any appropriate storage operating system including, for example, a write in-place file system may be enhanced for use in accordance with the inventive principles described herein. As such, where the term “WAFL” is employed, it should be taken broadly to refer to any storage operating system that is otherwise adaptable to the teachings of this invention.

FIG. 2 is a schematic block diagram of the storage operating system 200 that may be advantageously used with the present invention. The storage operating system comprises a series of software layers organized to form an integrated network protocol stack or, more generally, a multi-protocol engine that provides data paths for clients to access information stored on the storage system using block and file access protocols. The protocol stack includes a media access layer 210 of network drivers (e.g., gigabit Ethernet drivers) that interfaces to network protocol layers, such as the IP layer 212 and its supporting transport mechanisms, the TCP layer 214 and the User Datagram Protocol (UDP) layer 216. A file system protocol layer provides multi-protocol file access and, to that end, includes support for the Direct Access File System (DAFS) protocol 218, the NFS protocol 220, the CIFS protocol 222 and the Hypertext Transfer Protocol (HTTP) protocol 224. A VI layer 226 implements the VI architecture to provide direct access transport (DAT) capabilities, such as RDMA, as required by the DAFS protocol 218.

An iSCSI driver layer 228 provides block protocol access over the TCP/IP network protocol layers, while a FC driver layer 230 receives and transmits block access requests and responses to and from the storage system. The FC and iSCSI drivers provide FC-specific and iSCSI-specific access control to the blocks and, thus, manage exports of luns to either iSCSI or FCP or, alternatively, to both iSCSI and FCP when accessing the blocks on the storage system. In addition, the storage operating system includes a storage device manager embodied as a RAID subsystem 300 that manages the storage and retrieval of information to and from the volumes/disks in accordance with I/O operations, and a disk driver subsystem 250 that implements a disk access protocol such as, e.g., the SCSI protocol.

is Bridging the disk software layers with the integrated network protocol stack layers is a virtualization system that is implemented by a file system 280 interacting with virtualization modules illustratively embodied as, e.g., vdisk module 290 and SCSI target module 270. The vdisk module 290 is layered on the file system 280 to enable access by administrative interfaces, such as a user interface (UI) 275, in response to a user (system administrator) issuing commands to the storage system. The SCSI target module 270 is disposed between the FC and iSCSI drivers 228, 230 and the file system 280 to provide a translation layer of the virtualization system between the block (lun) space and the file system space, where luns are represented as blocks. The UI 275 is disposed over the storage operating system in a manner that enables administrative or user access to various layers and subsystems, such as the RAID subsystem 300.

The file system is illustratively a message-based system that provides volume management capabilities for use in access to the information stored on the storage devices, such as disks. That is, in addition to providing file system semantics, the file system 280 provides functions normally associated with a volume manager. These functions include (i) aggregation of the disks, (ii) aggregation of storage bandwidth of the disks, and (iii) reliability guarantees, such as mirroring and/or parity (RAID). The file system 280 illustratively implements the WAFL file system having an on-disk format representation that is block-based using, e.g., 4 kilobyte (kB) blocks and using index nodes (“inodes”) to identify files and file attributes (such as creation time, access permissions, size and block location). The file system uses files to store metadata describing the layout of its file system; these metadata files include, among others, an mode file. A file handle, i.e., an identifier that includes an mode number, is used to retrieve an mode from disk.

Operationally, a request from the client 110 is forwarded as a packet 150 over the computer network 140 and onto the storage system 120 where it is received at the network adapter 126. A network driver (of layer 210 or layer 230) processes the packet and, if appropriate, passes it on to a network protocol and file access layer for additional processing prior to forwarding to the file system layer 280. Here, the file system generates operations to load (retrieve) the requested data from disk 130 if it is not resident “in core”, i.e., in the memory 124. If the information is not in memory, the file system 280 indexes into the mode file using the mode number to access an appropriate entry and retrieve a logical VBN. The file system then passes a message structure including the logical VBN to the RAID subsystem 300, which maps that logical number to a disk block number (DBN) and sends the latter to an appropriate driver (e.g., SCSI) of the disk driver subsystem 250. The disk driver accesses the DBN from disk 130 and loads the requested data block(s) in memory 124 for processing by the storage system. Upon completion of the request, the storage system (and operating system) returns a reply to the client 110 over the network 140.

It should be noted that the software “path” through the storage operating system layers described above needed to perform data storage access for the client request received at the storage system may alternatively be implemented in hardware. That is, in an alternate embodiment of the invention, a storage access request data path may be implemented as logic circuitry embodied within a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). This type of hardware implementation increases the performance of the storage service provided by storage system 120 in response to a request issued by client 110. Moreover, in another alternate embodiment of the invention, the processing elements of adapters 126, 128 may be configured to offload some or all of the packet processing and storage access operations, respectively, from processor 122, to thereby increase the performance of the storage service provided by the system. It is expressly contemplated that the various processes, architectures and procedures described herein can be implemented in hardware, firmware or software.

As used herein, the term “storage operating system” generally refers to the computer-executable code operable to perform a storage function in a storage system, e.g., that manages data access and may, in the case of a file server, implement file system semantics. In this sense, the ONTAP software is an example of such a storage operating system implemented as a microkernel and including the WAFL layer to implement the WAFL file system semantics and manage data access. The storage operating system can also be implemented as an application program operating over a general-purpose operating system, such as UNIX® or Windows NT®, or as a general-purpose operating system with configurable functionality, which is configured for storage applications as described herein.

In addition, it will be understood to those skilled in the art that the inventive technique described herein may apply to any type of special-purpose (e.g., file server or filer) or general-purpose computer, including a standalone computer or portion thereof, embodied as or including a storage system 120. Moreover, the teachings of this invention can be adapted to a variety of storage system architectures including, but not limited to, a network-attached storage environment, a storage area network and disk assembly directly-attached to a client or host computer. The term “storage system” should therefore be taken broadly to include such arrangements in addition to any subsystems configured to perform a storage function and associated with other equipment or systems.

The present invention is implemented in the context of a configuration management framework used to implement the RAID subsystem 300 in the storage operating system 200. In a preferred embodiment, the configuration management framework provides an object-oriented approach to RAID configuration management, as described herein with respect to an implementation of the RAID subsystem. FIG. 3 is a schematic block diagram illustrating one or more modules or processes and threads of the RAID subsystem 300, wherein each process has, among other things, a (virtual) memory address space, executable code and data. A process is started with a single thread, but can create additional threads from any of its threads. The threads execute in the same memory address space and can therefore work concurrently on shared data. For example, an instantiator module implements a configuration (config) thread 310 adapted to maintain relationships among and invoke behaviors of decomposed software components (“RAID objects”) that collectively form the behaviors associated with a collection of (RAID) volumes on the storage system. In addition, an I/O manager module implements an I/O thread 320 configured to issue I/O transaction requests from the RAID subsystem to the disk driver subsystem and, upon completion, process the results.

A finite state machine (FSM) module or engine 330 is used to arbitrate a set of is events and states that a process or thread of the RAID subsystem may encounter. Transactional semantics isolate the behavior of state changes in the RAID subsystem from concurrent I/O operations. The framework provides a two-phase commit procedure, coordinated with updates to on-disk configuration data (“labels”). Errors during disk label updates are handled by aborting the transaction, releasing partially committed data and unwinding any pending state transitions. A state notification mechanism integrated with the FSM engine 330 propagates state changes through the threads in order to provide a coordinated behavior.

According to the configuration management framework, a volume comprises the aggregate behavior of a number of RAID objects. Each RAID object (“object”) comprises operational code and static state, such as configuration information, relating to the topology of the underlying physical storage devices, e.g., disks 130, contained in disk array 160. The objects are organized into a configuration tree with configuration interfaces defining a set of services provided by one or more processes of the RAID subsystem. Although the objects may be implemented in accordance with an object-oriented programming paradigm, the present invention is not limited to such an implementation. More broadly, the objects of the configuration tree refer to abstract entities representing a logical combination/configuration of the disks. That is, the objects are used to present a view of the underlying topology of the storage array managed by the RAID subsystem.

FIG. 4 is a schematic block diagram of an in core representation of an embodiment of a RAID configuration tree structure 400 in accordance with the configuration management framework. The configuration tree 400 comprises a plurality of objects arranged by the RAID subsystem into levels that cooperate to organize one or more physical disks into a single logical volume. References between objects (e.g., between a superior “parent” object and each of its subordinate “children” objects) are bi-directional memory address pointers that enable each child to reference its parent (and vice versa). These pointers are part of the metadata stored within each of the objects.

Objects have an associated type, with each object type providing its own implementation of the configuration interfaces. A volume is organized into a hierarchical conis figuration tree of objects that includes a tree object 402 responsible for coordinated behavior with the file system and a volume object 410 responsible for managing the RAID aspects of volume management. Specifically, the volume object 410 represents the (WAFL) file system at the highest level (i.e., root node) of the configuration tree 400. To that end, the volume object 410 stores metadata that describes a volume/file system, wherein the metadata includes information such as the name of the volume and address range (in physical blocks) of the volume. The name of the volume resides in a volume namespace that is exported by the UI 275 of the storage operating system 200. The logical address space of the file system is mapped to the physical (block) address space in the RAID subsystem 300.

The configuration tree 400 and, in particular, the volume object 410 represent a logical disk that is presented to the file system by the RAID subsystem as a “container” for the file system to store its data. That is, the objects of the configuration tree are organized to create an address space that resembles a single logical disk but, in reality, comprises a plurality of physical disks. In this context, the volume object 410 is equivalent to the tree object 402, wherein the tree object stores additional metadata about the logical volume that is presented to the file system. This additional metadata includes the type (level) of parity implementation configured for the particular volume (e.g., RAID-4, RAID-0, mirror_RAID-4, mirror_RAID-0, row-diagonal parity). Since the tree object is a one-to-one representation of the volume, the additional metadata stored in the tree object includes redundant information about the volume, such as its name and physical address/block range.

A next object level comprises a mirror object 420 that is responsible for coordinating one or more copies of the volume (termed “plexes”) in support of data mirroring. In synchronous data mirroring, two “mirror” copies are provided that are at all times synchronized. That is, changes to the data in one mirrored copy are immediately reflected in the other mirrored copy. The two identical mirrored copies have matching address spaces that are within the volume address space and that provide identical synchronized full copies of the data in the volume.

A plex object 430 is responsible for managing an instance of a copy of volume data and thus represents each mirrored copy within another object level of the configuration tree. Whereas the minor object 420 stores metadata that is used to coordinate one or more copies (or plexes) of the volume in support of data mirroring, each plex object 430 stores metadata that is used to manage an instance of a copy of volume data. The plex object may include an ordinal placement (e.g., 1, 2) indicating that, for example, a first part (1) of the address space is associated with a particular RAID group and that a second part (2) of the address space is associated with another RAID group.

A next object level comprises one or more RAID group objects 440 per plex object. Each RAID group object 440 contains metadata that provides data protection and I/O coordination over a set of disks. The metadata of the RAID group object includes information such as the number of disks within the RAID group and the address (block) range of each disk within the RAID group. In this context, a RAID group is defined as a number of disks and the address/block space associated with those disks. Finally, there is another object level comprising one or more disk objects 450 per RAID group object, wherein each disk object 450 contains metadata that provides data access to the physical disks 130.

The configuration tree 400 is constructed in the memory 124 of the storage system 120 by a label assimilation process 340 of the RAID subsystem 300. According to the assimilation process, each disk associated with a volume includes a disk label structure that describes its placement and association with that volume. The on-disk label is, in essence, self-describing information for each disk that is actively attached to the storage system 120. The labels are used to dynamically assemble the disks into a volume and to construct an in-core configuration tree for that volume, starting from the disk object level up to the volume object level. Therefore, a label on a disk identifies that disk's participation in a RAID group and, furthermore, that group's association with plex, minor and, ultimately, volume objects in the configuration tree. As described herein, the label is located in a well-known location of the disk so that it can be queried by the RAID subsystem in accordance with, e.g., a discovery process during a boot operation.

Each object type instance of the configuration tree 400 comprises the following components: service interfaces, committed transactional state, pre-committed transactional state and non-transactional state. The service interfaces comprise an application programming interface (API) that the object exports to other software components. In the illustrative embodiment, the service interfaces include initialization and destruction, child object management (add, replace), online/offline, transaction management (join, commit, abort, label I/O, state change notify), virtual block management, and I/O handling (context creation/deletion, resource management, I/O throttling). Each object type defines the commit, pre-committed, and non-transactional state that it holds. The transaction management interfaces are provided as a mechanism to create and modify transactional state in a manner that is coordinated across all objects in a volume.

The basic flow of control starts with a configuration management operation issued by, e.g., the file system 280 and received by the RAID subsystem 300. The file system passes the configuration management operation in the form of a message request that specifies a target volume and defines a named operation with specific parameters. The configuration thread 310 of the RAID subsystem receives the request and determines the object (e.g., volume, RAID group) of the configuration tree 400 for the volume to which the request is directed. The configuration thread then locates the tree object 402 for the volume and invokes relevant configuration operations using service interfaces of the appropriate object. When a service interface is invoked, the object is transparently “joined” to the request prior to activation of the interface. Joining of an object to a request results in copying of the currently committed state into a pre-committed state area (called the “trans” area of the object). The trans area is a portion of memory that records changes to the object that are pending commitment. The service interface makes its changes to the trans area. If the changes to the object result in a change of the state of the object, the FSM engine 330 is invoked.

The FSM engine 330 provides a critical component in managing the interrelationship between objects in a RAID volume. Specifically, the FSM engine defines the state/event pairs that are “legal” and, for each state/event, provides a mechanism to implement the invocation and determine any subsequent state transitions. In addition, the FSM engine provides tracing mechanisms to track the set of transitions that have occurred and provides object notification for pre-committed and committed state transitions. More specifically, the FSM engine 330 is responsible for determining the new state of the object (based upon a per object type state/event table) and invoking the state notification interface of its “superior” object in the volume hierarchy. The FSM engine includes an upward notification mechanism (e.g., from child to parent object) to notify the parent object about a state change in the child object.

When the configuration request completes all service interface invocations, it requests a label commit operation to persistently store the modified state. The label commit “pulls” data from the trans area in order to construct its new version of the label data. Label commit is deemed to be successful only if all labels in a plex can be successfully written. Once all labels have been successfully written, each object that has been joined to the request is responsible for copying its trans area data back to the committed state portion of the object. If labels are not successfully written, the trans area is discarded, any disk failures are identified and resulting configuration changes are initiated, the successfully written labels are re-written with the previous state, and the original configuration request is retried.

The present invention relates to a technique for mapping the capacity of storage devices, such as disks, into any RAID group of a volume of a storage system regardless of the location of the RAID group within a VBN space of the volume. To that end, the inventive technique separates disks and mapped VBN ranges, allowing for flexibility in the description and extension of RAID group capacities, while providing disk addition policies that support location-independent disk insertion into RAID groups. The inventive technique also is directed to the disk label structure that supports the provision of multiple VBN ranges within a RAID group and within individual disks.

Moreover, the technique provides file system support for allocation and topology management of the multiple mapped VBN ranges within disks and RAID groups, as well as noncontiguous VBN ranges across the RAID groups in the volume. Note that there is is a one-to-one mapping between the information stored on the disks in, e.g., DBN space, and the information organized by the file system in, e.g., VBN space. That is, each 4 kB file system block in the VBN space is mapped to a 4 kB disk block in the DBN space. An alternate embodiment of the invention may include multi-tiered mapping schemes, maps that are back-ended by multiple disks in a mirrored configuration or maps that are back-ended by non-disk storage devices (e.g., battery-backed memory).

FIG. 5 is a schematic block diagram of a (WAFL) file system map that defines a VBN space for its (file system) volume. The file system map is a data structure containing information maintained by the file system to correlate (“map”) the VBN space of the volume to the DBN space of all disks in the volume. Referring also to FIG. 4, data disk object 0 (d0) of RAID group object 0 (rg0) has DBNs 0-6 that are mapped to VBNs 0-6 of the volume. Similarly, d1 of rg0 has DBNs 0-6 that map to VBNs 7-13 of the volume. As disks are added to RAID groups of the volume, those disks are sequentially mapped to the VBN space, which likewise expands contiguously in accordance with a contiguous VBN-to-DBN mapping of disks in RAID groups. Notably, parity disks do not map into the file system VBN space.

Whereas the file system map contains VBN-to-DBN mapping information for all disks in the volume, a “raidmap” contains DBN-to-VBN mapping information for each disk in the volume. The raidmap is a data structure containing information maintained by the RAID subsystem to correlate the DBN space of a single disk to the VBN space of the volume. In particular, the information contained in the raidmap comprises mapping parameters that enable separation of DBN ranges on a disk from mapped VBN ranges of the volume. Each raidmap is stored on the disk label structure, i.e., a “RAID label”, of a disk and generally comprises a base offset into a VBN range of the volume, a base offset into a DBN range on the disk and a size (length) of the DBN-to-VBN mapping. Each RAID label is stored at a fixed location, e.g., at the end of a disk, and functions as an on-disk database of configuration information.

FIG. 6 is a schematic block diagram illustrating the format 600 of a disk. There is are various tiers of information stored on the disk, including control information outside of the DBN range of the disk and data within the DBN range. A section 620 of the disk may be used to store data within the DBN range comprising file system information, including user data (in the case of a data disk) or parity information (in the case of parity disk). Note that the DBN range may be logically apportioned into multiple pieces, per zo the invention, in order to support non-contiguous VBN ranges and/or VBN ranges associated with different volumes.

The control information outside the DBN range includes, but is not limited to, a table of contents that describes the entire layout of the disk (the locations of subsequent sections) and sections associated with disk ownership, RAID control information and other configuration data. In addition, as illustratively shown, a section 610 of the disk may be used to store kernel and boot image code of the storage operating system, and a section 630 of the disk may be used to store the RAID labels 630 and, in particular, the configuration information needed to describe how the particular disk fits into the volume.

The configuration information stored in the RAID label 630 describes the RAID group to which the disk belongs, along with all parent objects associated with the disk (e.g., plex, mirror, volume). Therefore, there is a region within the RAID label 630 for each parent object of the configuration tree associated with the disk storing the RAID label. The parent objects of the configuration tree (above the disk drives) are in-core memory objects that are created at the time the volume is assimilated. As noted, assimilation of a volume comprises reading (retrieving) the configuration information from all labels on all disks of the volume and then using that information to construct the configuration tree for the volume. The configuration information retrieved from the labels during assimilation includes the raidmaps used to describe the topology of the volume.

Although the raidmaps and their mapping ranges are illustratively not exposed to operators as configurable entities, the raidmap configuration may be important to system administrators when determining how to physically configure or alter a storage system. Disk addition techniques are knowledgeable about the current use of raidmap information is when determining when to place new disks into a volume. I/O task components (i.e, “raidio” structures) utilize raidmaps rather than directly referencing the disks. The raidmaps also support transactional behaviors when configuration operations execute on the volume.

FIGS. 7A-7E are schematic diagrams of raidmaps that may be advantageously used with the present invention. Each raidmap contains information indicating whether the disk is a data disk (within the VBN range) or a parity disk (outside the VBN range). Each raidmap comprises mapping parameters such as a starting disk block number (dbn_start), a starting volume block number (vbn_start) and a length of DBN-to-VBN mapping. Note that these raidmaps are illustrative examples only and that their contents may include additional information. For instance, each raidmap may further include a reference to a parent RAID object (the RAID group) and a child RAID object (the disk), the amount of valid data in the map where validity is determined by the RAID group implementation (e.g., unreconstructed data is considered invalid), a reference count on the number of users of the raidmap within the system and transactional information.

FIG. 7A depicts a first raidmap 700 for data disk 0 of RAID group 0 (e.g., rg0/d0/map0) and FIG. 7B depicts a first raidmap 720 for data disk 1 of RAID group 0 (rg0/d1/map0). Specifically, raidmap 700 contains mapping parameters including a starting disk block number (dbn_start) equal to 0, a starting volume block number (vbn_start) equal to 0 and a length of DBN-to-VBN mapping equal to 7. Note that the mapping parameters are specified in 4 kB blocks. Raidmap 720 specifies a starting disk block number (dbn_start) equal to 0, a starting volume block number (vbn_start) equal to 7 and a mapping length equal to 7. For purposes of discussion and description, the value of the length parameter is intentionally small. In a typical embodiment, the amount of space mapped by a single raidmap may cover hundreds of gigabytes or more, depending on the size of the physical or logical disk being mapped. Raidmap 700 resides in the RAID label 630 of data disk 0 and raidmap 720 resides in RAID label 630 of data disk 1. As described herein, there is sufficient space within each disk's RAID label for a plurality of raidmap “slots”, each slot describing a potential mapping from a volume VBN range to is the disk's DBN range. If a raidmap slot is not used, the associated raidmap data in the slot is marked “invalid”.

FIG. 7C depicts a raidmap 740 for a parity disk that specifies a starting disk block number (dbn_start) equal to 0 and a starting volume block number (vbn_start) equal to a sentinel value, such as −1. It should be noted that any sentinel value may be chosen that is outside of the DBN range. Since the parity disk does not map to the VBN space of a volume, the “−1” VBN offset is used to denote that the raidmap is directed to a non-mapping parity disk, such as the parity disk in a RAID-4 level group implementation. The capacity or size of the parity disk raidmap 740 is equal to the maximum size of the largest data disk of the RAID group. Data disks in a RAID group may vary in size and the parity disk must be large enough the cover the largest data disk of the RAID group. Therefore, the length parameter of a parity disk raidmap denotes the size of the parity disk, which must be at least as large as the largest data disk of the RAID group.

A write allocator 282 of the file system 280 is “aware” of the underlying (RAID) topology of the storage devices in order to achieve performance. To that end, the write allocator uses the raidmap and its description of that topology to issue I/O operations when accessing (via write allocation) data stored in the VBN range of a volume. A topology mechanism (e.g., the raidmap cache 170) exports the raidmap information from the RAID subsystem to the write allocator. Write allocation is directed to one RAID group at a time to enable writing of full stripes across the disks of the group. In the case of the illustrative RAID-4 level implementation, parity calculation for a write allocated stripe is performed only once. Notably, write allocation is based on RAID group layout rather than VBN space. That is, the VBN space is used internally within the file system to identify blocks, but not to allocate and write data to disk(s). Instead, the RAID group layout (size) is used for write allocation.

Typically, a maximum number of disks may be specified for a RAID group of a volume and, in the absence of a specified maximum, a default maximum number of disks for a RAID group may be established. For example, assume that the maximum RAID group size for a RAID-4 level implementation is 3 disks and RAID group 0 comprises is two data disks and one parity disk (not shown). Assume further that an operator wants to add a third data disk to the volume. The third data disk is thus added to a new RAID group, e.g., RAID group 1 (rg1), as data disk object 2 (d2), since the maximum number of disks in RAID group 0 has been reached.

Assume now that the operator adds two data disks (and one parity disk) to RAID group 1. These data disk objects (d2 and d3) are mapped to the VBN space of the volume in a manner that is contiguous with the data disk objects of RAID group object 0. That is, d2 has DBNs 0-6 that map to VBNs 14-20 of the volume and d3 has DBNs 0-6 that map to VBNs 21-27 of the volume. Once the maximum number of disks in a RAID group has been satisfied and additional disks are inserted into a next RAID group, the size of a previous RAID group typically cannot change, e.g., cannot increase. This is due, in part, to the contiguous VBN-to-DBN mapping for, e.g., write allocation in the file system. In other words, VBN ranges typically cannot be mixed within RAID groups.

According to an aspect of the inventive technique, a new disk may be added to a RAID group (e.g., RAID group object 0) that is not the most recently established, i.e., the “last” RAID group (e.g., RAID group object 1), of a volume. The ability to add a new disk to a RAID group that is not the last RAID group is achieved because each disk stores a raidmap describing the DBN-to-VBN mapping of its blocks and because that mapping information (along with other configuration information) is “cached” (stored) in memory (raidmap cache 170) for use by the file system. Specifically, the write allocator advantageously uses the mapping parameters of the raidmap to determine the non-contiguous VBN-to-DBN mapping of a disk (e.g., the disk newly inserted) of the RAID group. Configuration changes to the physical disks managed by the RAID subsystem are reflected as changed configuration information that is cached in raidmap cache 170 for use by the write allocator 282 of the file system 280. As long as the write allocator is aware of the underlying changed topology (via the raidmaps), there is no performance impact by having noncontiguous VBN-to-DBN mappings in a RAID group.

For example, assume data disk object d4 is added to RAID group object 0 (rg0) even though data disk objects d2-d3 are members of RAID group object 1. FIG. 7D depicts a first raidmap 760 for d4 of rg0 (e.g., rg0/d4/map0). Raidmap 760 specifies a starting disk block number (dbn_start) equal to 0, a starting volume block number (vbn_start) equal to 28 and a length of DBN-to-VBN mapping equal to 7. Thus, the DBN-to-VBN mapping for newly inserted d4 is DBNs 0-6 mapped to VBNs 28-34. Although this results in a noncontiguous VBN-to-DBN mapping within RAID group 0, the raidmaps of the present invention enable the RAID subsystem to support such noncontiguous mappings and, in particular, the ability to have multiple VBN ranges per RAID group.

Another aspect of the present invention relates to the mapping of multiple VBN ranges to the DBN space of a disk through the ability to store more than one raidmap in a RAID label on each disk. This aspect of the invention is particularly useful in the event of a failure to a disk of a RAID group and the replacement of that failed disk with a larger disk. For example, assume data disk d0 of RAID group 0 fails and a new disk is added to RAID group 0 to replace the failed disk. The data stored on the failed disk is reconstructed on the replacement disk in accordance with a conventional reconstruction process using the constituent data/parity stored on the other disks of the RAID group. If the replacement disk has the same size as the failed disk, then the DBN-to-VBN mapping of the replacement disk is similar to that of the failed disk. However, if the replacement disk is larger than the failed disk, the present invention enables use of the additional space on the larger disk through the use of second raidmap for the disk.

There is initially one raidmap 700 for data disk object 0 of RAID group object 0 (rg0/d0/map0). If d0 fails and that disk is replaced with a larger disk, the first portion of the larger disk is used to reconstruct the failed d0, such that DBNs 0-6 are mapped to VBNs 0-6 in the volume. In addition, the second portion of the larger disk is used to map into the volume at the end of the VBN range that has been previously mapped. FIG. 7E depicts a second raidmap 780 for data disk object 0 of RAID group object 0 (e.g., rg0/d0/map1) pertaining to the second portion of the larger disk inserted into RAID group 0. The raidmap 780 specifies a starting disk block number (dbn_start) equal to 7, a starting volume block number (vbn_start) equal to 35 and a length of DBN-to-VBN mapping equal to 10.

Advantageously, this aspect of the present invention provides a means for expanding the storage space of an existing file system when mapping the capacity of a new disk into a volume, wherein the new disk is larger than the disks of the volume, and making use of the additional space on the larger disk. An example of such a situation involves replacing a failed disk with a larger disk of a RAID group. The expansion aspect of the invention allows efficient use of inevitable increases in the sizes of disks that may be used as replacement disks for previously installed disks of a storage system. The expansion aspect of the present invention also provides a more efficient approach to utilizing the extra space on replacement disks as compared to prior approaches by allowing use of the additional space on replacement disks in an efficient manner that is “online” and involves no disruption to the file service provided by the storage system to an operator/client.

Therefore when mapping the capacity of a disk into any RAID group of a volume, such as when replacing a failed disk with a larger disk, the present invention enables creation of (i) a first raidmap to reconstruct the failed disk using a first portion of the large disk and (ii) a second raidmap to map a second portion of the large disk into the VBN space of the file system volume. To that end, the invention allows storage of two raidmaps in the RAID label of a particular disk. As noted, there is space within each RAID label on each disk for many raidmaps.

Note that if a disk fails, a disk error-handling process modifies the state of the raidmap to indicate that maps associated with the disk are “stale” (no longer valid). Disk error handling “flips” the stale map with a new map indicating that a “hole” exists in the VBN space corresponding to the size of the stale map. The stale map remains in memory until all uses by raidio structures and other components (e.g., the raidmap cache) of the RAID subsystem have terminated. Meanwhile, a new map (marked as “unmapped” space) is integrated into the RAID group's raidmap configuration. The raidio structures and components recognize the stale map condition as part of their error handling, and typically abort and restart with the RAID group's updated raidmap configuration.

Flipping of a map may occur when a disk is inserted into a RAID group to replace is a failed disk or when a disk is removed from a RAID group. Map flipping is designed to operate transactionally, allowing for concurrent I/O operations to view the configuration in a coherent manner. When new disks are added to extend RAID group capacity, trans-actional behaviors and file system semantics prevent access to the newly added VBN range until the operation has been committed to disk.

Another advantage of the expansion feature of the invention is the ability to move an existing volume from smaller disks to larger disks using synchronous minoring and the additional mapping capabilities within those larger disks. For example, assume it is desired to “mirror” an existing volume with disks of capacity size X, e.g., 36 gigabytes (GB), to a new volume with disks of capacity 2X, e.g., 72 GB. In the illustrative embodiment, the RAID subsystem 300 desires a mirroring behavior using exact sized disks, implying that only half of the disk capacity is initially used in the new volume minor. Once the minor is synchronized, the original volume mirror may be disabled, leaving the volume with only 2X disks. The inventive technique enables the volume to extend the additional capacity, resulting in multiple VBN ranges for the RAID group.

FIG. 8 is a schematic block diagram of an in-core representation of another embodiment of a RAID configuration tree 800 in accordance with the configuration management framework. As with the configuration tree 400, configuration tree 800 includes a tree object 802 responsible for coordinated behavior with the file system, a volume object 810 responsible for managing the RAID aspects of volume management and a minor object 820 responsible for coordinating one or more plexes in support of data mirroring. Here, the configuration tree 800 and, in particular, the volume object 810 represent a logical disk that is presented to the file system by the RAID subsystem as a synchronous minor container for the file system to store its data. Therefore, two plex objects 830 (plex 0 and plex 1) are provided, wherein each plex essentially manages a full copy of the volume data. In addition, the configuration tree 800 includes four RAID group objects 840 responsible for data protection and I/O coordination over a set of disks, and a plurality of disk objects 850 responsible for data access to the physical disks 130.

Assume that the existing plex (plex 0) has disks of capacity size X (e.g., 36 GB) and that the new “mirrored” plex (plex 1) has disks of capacity 2X (e.g., 72 GB). Because of the mirroring behavior of desired by the RAID subsystem 300, there is a one-to-one correspondence between each disk 850 of each plex 830, i.e., the disks contain the same data and map into the same VBN space. Thus, if RAID group object rg0 has data disk objects d0, d1 and d4, then rg0′ has d0′, d1′ and d4′. In addition, the mirrored disks must have the same sized raidmaps; therefore, initially only an upper portion (36 GB) of the 72 GB disks are used to provide symmetry with the disks in the other plex.

A resynchronization (resync) operation is then performed which essentially copies all the data with the original 36 GB disks to the mirrored 72 GB disks. While the resync operation is in progress, an operator/client has full access to the data stored on the original 36 GB disks. From the perspective of the file system, no changes have occurred to the underlying topology of the volume. That is, the file system has access to its entire VBN space with respect to reading or writing data to the mapped DBNs on the disks. Transparently, though, the RAID subsystem is copying the data from the original 36 GB disks to the mirrored 72 GB disks.

Once the data is fully copied to the mirrored plex, a normal mirrored state is reached wherein there is full redundancy such that any access (read or write operation) to data served by the storage system occurs on disks of both plexes. However, the additional storage space on the 72 GB disks cannot be used because there are no equivalent spaces on the disks of the other original plex. Since all the user data is now stored on the 72 GB disks of the second plex, the original plex and its constituent disks can be “destroyed” and replaced with similarly sized 72 GB disks. Here, a goal is to move or migrate an existing volume having 36 GB disks to larger 72 GB disks while also migrating the volume from an unmirrored to mirrored configuration. Once the original plex is destroyed, the additional space on the 72 GB disks can be used and, therefore, mapped into the VBN space of the volume since there is no longer any restriction to its use. As a result, the file system VBN space can be “dynamically” increased to take advantage of the additional physical storage space (DBN space) on the newly inserted 72 GB disks.

According to the invention, each 72 GB disk has two raidmaps used to map the is physical disk space (DBN) on the disk to the volume space (VBN) in a manner that is transparent to the file system, as long as that configuration information is cached in memory for use by the file system. That is, using the raidmaps and configuration information, the file system can read or write to all the mapped ranges on the disks. Since the original plex has been destroyed and the 36 GB disks have been removed from the storage system, those disks can be replaced with 72 GB disks and recreate the original plex using those disks. Thereafter, the data stored on the other plex is copied over onto the newly created plex in accordance with a mirror resync operation, wherein the data that is copied includes the raidmaps. Throughout the entire process of replacing original 36 GB disks with larger 72 GB disks, the file system continues to provide file service for the data stored on the disks and, in fact, the file system is unaware of the configuration change.

By providing two full copies of the data for a volume, the use of mirroring in connection with the present invention advantageously enables (i) “off-lining” of a plex (bringing the plex offline), (ii) unplugging of the disks of a disk shelf from the storage system, (iii) relocating of the disk shelf to another location, (iv) reconnecting of the disk shelf and disks with the storage system and then (v) “onlining” the plex (bringing the plex online) without disturbing file service to the information stored on the volume. The present invention obviates the burdensome procedure of the prior art because only one volume is utilized between the two plexes.

Assume now that a disk in one plex (e.g., d0 in plex 0) is replaced by a yet larger disk d0. In order to extend the DBN-to-VBN mappings on replacement disk d0 to utilize the extra space on that disk, the mirrored disk in the mirrored plex (e.g. d0′ in plex 1) must also be extended to utilize the equivalent amount of extra space in order to maintain symmetry between the mirrored copies of data. Therefore, a restriction with respect to the present invention when utilized in a mirroring arrangement is that the additional space provided by a larger replacement disk may not be utilized until the “mirrored” disk is replaced with an equivalently sized disk.

Advantageously, the present invention isolates disks from VBN ranges, providing is flexibility in RAID group topologies. Isolation of VBN ranges from disks further allows for dynamic extension of the VBN range at the RAID level without requiring reorganization of the existing blocks in the file system. The inventive technique supports dynamic extension of capacity using existing, but formerly unused, disk space. Moreover, the on-disk label structure contains placeholders for multiple per-disk VBN range data, thereby zo facilitating instantiation of the raidmap information when a volume is brought into the system during initialization.

While there has been shown and described an illustrative embodiment for mapping the capacity of disks into any RAID group location within a VBN space of a volume of a storage system, it is to be understood that there are other advantages provided by the technique of the present invention. For example, another application of the present invention enables a disk to utilize its physical disk space (DBN ranges) among different volumes of the storage system. Typically, the physical DBN storage space of a disk is restricted to residing in the same volume. The use of multiple raidmaps per disk allows a second portion of the DBN space on a disk to reside in another volume that is different from the volume within which a first portion of the disk's DBN space resides. The configuration information stored in the RAID label must be extended to differentiate between the set of objects associated with a first portion of the physical disk space and the set of objects associated with the second portion of the physical disk space.

In summary, restrictions applicable to previous RAID subsystems include (i) each disk had exactly one raidmap stored in each RAID label on the disk and (ii) the ordering of disks as they appeared in the file system map is exactly the same as the ordering of disks in the RAID groups. The present invention relaxes those restrictions by (i) allowing each disk to have one or more raidmaps in each RAID label and (ii) allowing ordering of disks as they appear in the file system map to be different from the ordering of disks in the RAID groups (i.e., a disk can be added into a RAID group that is other than the last established RAID group).

A preferred embodiment of the invention has been described herein with reference to a file server having a storage operating system with a file system layer and a RAID subsystem (among other components), which manages file semantics in order to access data organized in files. It should be understood, however, that the invention can be practiced in any system or device that maps the capacity of disks into any RAID group of a volume of a storage system, particularly in light of configuration management changes. One type of system or device in which the invention can be embodied is designed to perform a data storage function, and if so, may perform data-related operations, e.g., in response to data access requests. Such requests may use file-based and/or block-based semantics, depending on the implementation and, correspondingly, the system or device may organize data in files or in another manner. Moreover, such systems and devices may or may not incorporate features and functions described herein, such as, for example, a file system layer or a RAID subsystem, or may combine or otherwise modify their operation, without departing from the principles of the invention.

The foregoing description has been directed to specific embodiments of this invention. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. For instance, it is expressly contemplated that the teachings of this invention can be implemented as software, including a computer-readable medium having program instructions executing on a computer, hardware, firmware, or a combination thereof. In addition, it is understood that the data structures described herein can include additional information while remaining within the scope of the present invention. Accordingly this description is to be taken only by way of example and not to otherwise limit the scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention. 

1. A method for operating a computer storage system, comprising: assigning a range of volume block numbers (VBNs) to one or more volumes of the computer storage system; assigning storage device block numbers (DBNs) to a first storage device of a plurality of storage devices of the computer storage system; creating a storage device label structure for the first storage device; and storing, in the storage device label structure, a plurality of raidmaps for the first storage device, each raidmap of the plurality of raidmaps comprising mapping parameters describing a different mapping from the VBNs of the one or more volumes to the DBNs of the first storage device.
 2. The method as in claim 1, further comprising: storing the storage device label on the first storage device.
 3. The method as in claim 1, wherein each raidmap comprises one or more mapping parameter sets that map one or more of the VBNs into corresponding DBNs of the DBNs of the first storage device.
 4. The method as in claim 1, further comprising: adding extra storage space by replacing the first storage device of the plurality of storage devices with a larger storage device; and mapping new VBNs into DBNs of the extra storage space.
 5. The method as in claim 1, wherein the storage device label comprises a RAID label.
 6. The method as in claim 1, further comprising: replacing the first storage device of the plurality of storage devices with a larger storage device.
 7. The method as in claim 1, wherein the first raidmap comprises a base offset into the VBN range.
 8. The method as in claim 1, wherein the first raidmap comprises a base offset into a DBN range of the first storage device.
 9. The method as in claim 1, further comprising: using an array of writable storage device media as the first storage device.
 10. The method as in claim 1, further comprising: using video tape as the first storage device.
 11. The method as in claim 1, further comprising: using an optical device as the first storage device.
 12. The method as in claim 1, further comprising: using a DVD as the first storage device.
 13. The method as in claim 1, further comprising: using a magnetic tape as the first storage device.
 14. The method as in claim 1, further comprising: using a bubble memory as the first storage device.
 15. The method as in claim 1, further comprising: using an electronic random access memory as the first storage device.
 16. The method as in claim 1, further comprising: using micro-electro mechanical device as the first storage device.
 17. The method as in claim 1, further comprising: using a magnetic disk as the first storage device.
 18. The method as in claim 1, further comprising: using a RAID array of magnetic disks as the first storage device.
 19. A method for operating a computer storage system, comprising: assigning a range of volume block numbers (VBNs) to one or more volumes of the computer storage system; assigning storage device block numbers (DBNs) to a first storage device of a plurality of storage devices of the computer storage system; and storing a plurality of raidmaps for the first storage device, each raidmap comprising information describing a different mapping of one or more of the DBNs of the first storage device to the VBNs of the one or more volumes.
 20. The method of claim 19, further comprising: storing the plurality of raidmaps on the first storage device.
 21. A computer readable storage media configured to store executable program instructions to be executed by a processor, comprising: program instructions that assign a range of volume block numbers (VBNs) to one or more volumes of a computer; program instructions that assign storage device block numbers (DBNs) to a first storage device of a plurality of storage devices of the computer; program instructions that create a storage device label structure for the first storage device; and program instructions that store, in the storage device label structure, a plurality of raidmaps for the first storage device, each raidmap of the plurality of raidmaps comprising mapping parameters describing a different mapping from the VBNs of the one or more volumes to the DBNs of the first storage device.
 22. A computer storage system apparatus, comprising: a processor configured to execute a storage operating system of the computer storage system apparatus, the storage operating system configured to assign a range of volume block numbers (VBNs) to one or more volumes of the computer storage system apparatus; the storage operating system further configured to assign storage device block numbers (DBNs) to a first storage device of a plurality of storage devices of the computer storage system apparatus; and the storage operating system further configured to maintain a structure configured to store a plurality of raidmaps for the first storage device, each raidmap of the plurality of raidmaps comprising mapping parameters that describe a different mapping from the VBNs of the one or more volumes to the DBNs of the first storage device.
 23. The apparatus as in claim 22, wherein the structure comprises a storage device label.
 24. The apparatus as in claim 22, wherein each raidmap comprises one or more mapping parameter sets that map one or more of the VBNs into corresponding DBNs of the DBNs of the first storage device.
 25. The apparatus as in claim 22, wherein the storage operating system is further configured to map new VBNs into DBNs of a second storage device added to the plurality of storage devices by replacing the first storage device with the second storage device, wherein a first raidmap of the plurality of raidmaps corresponds to a first portion of the second storage device and wherein a second raidmap of the plurality of raidmaps corresponds to a second portion of the second storage device.
 26. The apparatus as in claim 22, wherein the first raidmap comprises a base offset into a VBN range of the one or more volumes.
 27. The apparatus as in claim 22, wherein the structure is stored on one or more of the plurality of storage devices.
 28. The apparatus as in claim 22, wherein the raidmap comprises a base offset into a DBN range of the first storage device.
 29. The apparatus as in claim 22, wherein the structure comprises placeholders for each raidmap.
 30. The apparatus as in claim 22, further comprising: an array of writable storage device media used as the first storage device.
 31. The apparatus as in claim 22, further comprising: a video tape used as the first storage device.
 32. The apparatus as in claim 22, further comprising: an optical device used as the first storage device.
 33. The apparatus as in claim 25, wherein the first portion corresponds to the first storage device.
 34. The apparatus as in claim 22, further comprising: a magnetic tape used as the first storage device.
 35. The apparatus as in claim 22, further comprising: a bubble memory used as the first storage device.
 36. The apparatus as in claim 22, further comprising: an electronic random access memory used as the first storage device.
 37. The apparatus as in claim 22, further comprising: micro-electro mechanical device used as the first storage device.
 38. The apparatus as in claim 22, further comprising: a magnetic disk used as the first storage device.
 39. The apparatus as in claim 22, further comprising: a RAID array of magnetic disks used as the first storage device.
 40. A computer storage system, comprising: a processor configured to execute a storage operating system of the computer storage system, the storage operating system configured to assign a range of volume block numbers (VBNs) of a VBN space to one or more volumes; the storage operating system further configured to assign storage device block numbers (DBNs) to a first storage device of a plurality of storage devices operatively connected to the computer storage system; a RAID subsystem of the computer storage system configured to maintain a first mapping parameter to map a first range of the VBNs to a first range of the DBNs of the first storage device; the RAID subsystem further configured to maintain a second mapping parameter to map a second range of the VBNs to a second range of the DBNs of a second storage device of the plurality of storage devices; the RAID subsystem further configured to maintain a structure to store the first mapping parameter and the second mapping parameter; and the storage operating system further configured to reconstruct the first storage device on the second storage device, wherein the first mapping parameter is mapped to a first portion of the second storage device, and wherein the second mapping parameter is mapped to a second portion of the second storage device, the second portion used for an extended range of the VBN space.
 41. The computer storage system of claim 40, further comprising: a write allocator configured to store the structure on the first storage device. 